In general, a small-sized camera module is mounted in mobile terminals, such as smartphones. A lens driving apparatus having an autofocus function of automatically performing focusing during capturing a subject (hereinafter referred to as “AF function”. AF: Auto Focus) is applied in such a camera module (see, for example, Patent Literatures (hereinafter, abbreviated as PTLS) 1 and 2).
The auto-focusing lens driving apparatus includes, for example, an auto-focusing coil (hereinafter referred to as “AF coil”) disposed at the periphery of the lens part, an auto-focusing magnet (hereinafter referred to as “AF magnet”) disposed to be radially spaced apart from the AF coil, and an elastic supporting part (e.g., plate spring) for elastically supporting an autofocus movable part (hereinafter referred to as “AF movable part”) including the lens part and the AF coil, for example, with respect to an autofocus fixing part (hereinafter referred to as “AF fixing part”) including the AF magnet. Focusing is automatically carried out by moving the AF movable part with respect to the AF fixing part in the optical-axis direction by utilizing a driving force of a voice coil motor composed of the AF coil and the AF magnet. Note that, the AF fixing part may include the AF coil and the AF movable part may include the AF magnet.
In lens driving apparatuses disclosed in PTLS 1 and 2, a case which serves as a casing of the lens driving apparatus is formed of a magnetic material, and an AF magnet is disposed on the inner surface of the case. Since the case functions as a yoke which forms a magnetic circuit with the AF magnet, leakage flux from the AF magnet is reduced. This increases magnetic lines of force which cross the AF coil, so that the driving efficiency of the voice coil motor improves.